Thanks again Mike. This circuit is from the page you gave me on Transistor Amplifiers from Talking Electronics.So i am trying to understand how it works . Ideally I want to develop it further to make a light sensor for 24V but trying to model these things in LTSpice is proving difficult . The Tutes I have found so far are not very good . Probably good enough if you have done 3 years of Electrical Engineering at Uni but I only did the first year so I find it difficult to follow.
There will be better explanations of PWL ,.step parameter ,and other commands I am sure but I haven't found them yet .